Hexafluorophosphate HOTT

S- 1 -Oxido-2-pyridinyl)-1,1,3,3-tetramethylthiouronium Hexafluorophosphate (HOTT), 463 CioH,602... 

Indole carboxylic acid 187 was converted via a Barton ester to fused indole 194 (11 examples, 5-79% yield). Barton ester 189 was formed by treatment of indole 187 with S-(l-oxido-2-pyridinyl)-l,l,3,3-tetramethyl thiouronium hexafluorophosphate (188, Garner s HOTT reagent) in the absence of light. Upon refluxing in MeCN, the Barton ester 189 decomposes to give nucleophilic ethyl radical 190, which adds to the unsubstituted carbon of alkyne 191 furnishing vinyl radical 192.This species cyclizes onto the C2 position of the indole to provide 193, which aromatizes to dehver the final product 194. The sequence proceeds without the need for an initiator or metal catalyst (14JOC5903). 

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